With the advent of semiconductor devices having increasingly large component densities, the removal of heat generated by these devices has become an increasingly challenging technical issue. Highly available computer systems, to prolong a customer's investment, are designed to both be maintained for long periods and to be easily maintained over time. This makes it preferable that a computer system is well cooled across all of its components on each board, and that the computer can quickly and readily accept replacements for malfunctioning boards. Typical processor boards sometimes include multiple CPU modules, application-specific integrated circuits, and one or more types of memory such as static random access memory, as well as dc-dc converters, all of which have different and extreme power dissipation requirements. Adding to the complexity, the variety of chip types on typical processor boards provides for chip surfaces at a variety of heights off the board's surface.
In the past, the low power dissipation of the processors accommodated the use of low cost, air-cooled heat sinks that require minimal re-design effort. However, with higher dissipation requirements comes more complex cooling systems that make both the even cooling requirements and the serviceability of a board a more complex issue. In particular, different components stand up off the board with different heights, which causes board-wide cooling systems to cool different components to different degrees, even if the components' power dissipation levels are similar, which typically is not the case.
Spray-cooling technologies can offer high dissipation levels that meet extreme cooling requirements. With reference to FIG. 1, in spray cooling, an inert spray coolant from a reservoir 11 is preferably sprayed by sprayers 13 onto chips 15 mounted on a printed circuit board 17. The coolant preferably evaporates, dissipating heat within the chip. The sprayers and chips, and the board, are mounted within sealed cases 19 fixed within a computer system. The sprayed coolant is typically gathered and cooled within a condenser 21, and then routed back to the reservoir by a pump 23.
The cases are evacuated systems with robust closure systems. Access to the components for maintenance can typically be had only through extensive disassembly of the computer system and case, which is significantly more time consuming and costly than the maintenance of standard air-cooled chips. Thus, for a liquid cooled board, board replacement becomes a complex issue that must deal with the presence of liquid, and potentially the need for an evacuated system.
Additionally, the repair or replacement of the cooling system, which includes a multitude of sprayers, can be time consuming and expensive. To minimize computer down time when a sprayer fails to function properly, a complete replacement of the cooling system can be used. However, the costs of such a replacement can be high because a number of functional sprayers that must be discarded with the dysfunctional sprayer.
Furthermore, it is known that the thermal performance achieved from spray cooling is dependant upon the distance between the firing nozzle and the hot surface. A greater distance allows for more of the cooling fluid to evaporate prior to reaching the chip. Furthermore, drag reduces the speed of the droplets, allowing even more cooling fluid to evaporate prior to reaching the chip. The evaporation of cooling fluid prior to reaching the chip reduces the fluid flow rate received by the chip, and thus reduces the thermal performance of the spray-cooling system. The reduced speed of the droplets also reduces their momentum, and thus their ability to penetrate vapor barriers, such as can form at near-maximum levels of heat flux for a spray-cooling system.
Since processor boards can and often do contain components of dissimilar heights, it has been suggested that the hottest component be used as the reference component to determine the sprayjet cartridge-to-board spacing. The primary disadvantage of this technique is that fluid may be delivered inefficiently to other hot components of markedly different heights from the reference component.
Accordingly, there has existed a need for an easily maintainable spray-cooling system that maximizes spray-cooling efficiency for a plurality of components on a printed circuit board, while minimizing system cost. Preferred embodiments of the present invention satisfy these and other needs, and provide further related advantages.